To protect the security of the computer, in addition to anti-virus software, another means is a firewall. The firewall has two main purposes: 1) To resist the attack of the external network on the local computer; 2) To effectively control the access of the local program to the Internet. It's a pity that Windows' built-in firewall has a single function and poor usability, so there are a large number of third-party firewall programs. Of course, all third-party firewalls implement corresponding functions based on the operating mechanism of Windows' built-in firewall.

When your Mac computer is connected to the Internet, countless connections will be quietly built in the background. Once some application connects to the Internet, it can send any information that it wants to send to any place in the world. In order to monitor these connections, better maintain our privacy security, and especially withstand the tracking software, Trojans, or other types of malware, we usually have to use the boring and difficult to use firewall software. Even worse, the inbuilt firewall program of Mac OS is only able to control incoming connections, has no monitoring and controlling capabilities for outgoing connections.